A child's inability to get a good night's sleep has become a major public health concern. Among children of preschool age and older, sleep disturbances are linked to daytime behavior problems, sleepiness and poor attention, and academic underachievement. Very little, by contrast, is known about the impact of sleep problems in infancy on infant day time functioning. This is noteworthy, in light of the fact that significant sleep disruptions can become evident in the first year of life, tend to remain stable over time, and present as a chief complaint of parents to pediatricians. This application is consistent with the stated mission of NICHD and responds to PA-05-046, Research on Sleep and Sleep Disorders and has three inter-related aims. Aim 1: To investigate linkages between infant sleep quality, infant socio-emotional and cognitive developmental outcomes, and parent-infant relationship outcomes during the infant's first two years. Outcomes of interest include infant stress reactivity (cortisol), emotion regulation in responses to stress, security of infant-mother attachment, infant behavior problems and behavior competencies, quality of compliance to maternal directives, information processing ability, and quality of maternal-infant emotional availability during interaction. In addressing aim 1, we will document individual differences in when, during the course of the first two years, linkages between infant sleep quality and infant developmental outcomes emerge, to what degree they are associated with severity and chronicity of sleep disruption, and whether and when these linkages dissipate if infants develop more organized, regulated sleep with age. Aim 2: To examine the role of parenting practices in sleep contexts in predicting infant sleep quality, and the role of infant temperamental difficulty (from parent report and observational assessment) in moderating these relations. Aim 3: To examine parents' adaptation to infant sleep behavior, the determinants of such adaptation, and the role of parental adaptation to infant sleep in predicting infant sleep quality and infant and parent daytime functioning. The focus on parental adaptation is based on emergent information that whether or not a child is identified with a sleep problem, and whether that problem has consequences beyond the sleep context, depends greatly upon parents' perception and tolerance of child sleep behavior. This focus is also rooted in theoretical formulations that developmental problems in infancy and early childhood can only be understood in the context of the child's relationships with caregivers. This study will provide important information about the inter-linkages between infant sleep quality and infant day time outcomes, and the role of parenting and parental adaptation in accounting for these links. PUBLIC HEALTH RELEVANCE: A child's inability to get a good night's sleep is major public health concern. Sleep disruption in children of preschool age and older is linked to behavior problems, daytime sleepiness, poor attention, and academic underachievement. Very little, by contrast, is known about the impact of infant sleep problems, or the role of parenting in relation to them, on infant cognitive and emotional development. This study's findings will have immediate relevance for parents and health care providers because it will clarify the most important predictors of infant sleep behavior and provide suggestions for pediatric practice.